The present invention relates to the field of bags or packages containing complementary closure strips for allowing successive opening and closing.
More particularly, the present invention concerns the field of machines for automatically forming, filling, and closing such packaging formed of thermoplastic film and including complimentary male and female closure strips. Machinery of this kind is often referred to as FFS machinery.
Many machines of this type have already been proposed (see, for example EP-A-528721 and U.S. Pat. No. 4,894,975. As shown in FIG. 1, most of these machines include a forming neck (10), which receives incoming film (F) in a flat state as it is supplied by an unrolling mechanism (20) and outputs the film (F) formed into a tube; a filling spout (30) extending into said forming neck (10) and, hence, into said tube; a mechanism (40) for positioning closure strips (P) and attaching them to the film (F); a mechanism (50) for longitudinal sealing the tube closed; and a mechanism (60) suitable for sequentially forming a first transverse weld (61) before introduction of a product into the tube through the filling spout (30) and a second transverse weld (62) after the product has been introduced into the tube, to form a package around the product.
Most of the machines proposed so far are designed to receive the closure strips (P) in the longitudinal direction, that is, parallel to the direction in which the film (F) moves. However, machines with longitudinal strips have the disadvantage of limiting the height of bags that can be obtained. This height is, in fact, equal to half the circumference of the forming neck. Moreover, the packages obtained on these machines sometimes have defects in sealing. This is due to the fact that the mechanism for transverse sealing (60) must operate through the excessive thickness formed by the longitudinal profiles (P).
Attempts to remedy this situation have been made by not placing the closure strips (P) longitudinally, i.e. in the direction of the film movement, but rather placing the strips transversely, that is, perpendicular to the direction of movement of the film (F).
Early attempts are described in U.S. Pat. No. 4,617,683 and 4,655,862. These patents, which issued more than a decade ago, offered two solutions for positioning closure strips (P) transversely onto the film (F) in a flat state, before the film arrives at the forming neck (10).
The attempts proposed were initially considered promising. Ultimately, however, they failed to provide satisfactory results and were rejected. In particular, it was observed that the mechanisms described in the patents did not always allow the transverse ,strips to be placed completely straight across the film. As a result, it was often difficult for the complementary sections to be fitted together.
Other solutions were subsequently proposed in an attempt to overcome the inconveniences resulting from utilizing the mechanisms described in the cited patents. In U.S. Pat. Nos. 4,666,536, 4,701,361, 4,878,987, 4,617,683, 4,655,862, 4,844,759, 5,111,643, 4,709,398, and 4,909,017, for example, other mechanisms intended to place transverse closure strips on a film have been proposed.
In the applicant""s own patent application FR-A-2 745 261, a machine for forming packages from film is described that includes a mechanism for placing closure strips transversely onto a film, the strips being formed in combination with a straight guide that has been placed transversely on it and designed to allow positioning a closure strip precisely across the film, and a mechanism for gripping the upstream end of the closure strip and moving transversely along the guide, to guide the closure strip into the latter by traction on the upstream end of the closure.
To date, none of these attempts have met with manufacturing success as far as known by the inventor hereof. This disaffection on the part of manufacturers with machines using transverse strips appears to be particularly attributable to the fact that, although these machines allow a certain degree of latitude in defining the height of bags, it is also true that these machines in principle require bags with a constant width, equal to half the circumference of the forming neck.
The principle object of the present invention is to provide an improved machine for forming packages of film including complementary closure strips placed transversely on the film that allows unrestricted variation of the width of the bags obtained.
According to the present invention, this objective is achieved by means of a machine characterized by the fact that it includes a removable forming neck, so that the user can install a variety of forming necks of different diameters and a mechanism for attaching closure strips having a length of up to half the circumference of the largest forming neck.
The present invention further relates to a process for forming packages and the closure means for this purpose.